1. Field of the Invention
This invention relates to a magnetic head assembly for a magnetic disk recording and playback apparatus.
2. Description of the Prior Art
There is known a magnetic head assembly for reading and writing information on both sides of a magnetic disk, as disclosed, for example, in U.S. Pat. No. 4,151,573. Its general construction is shown in FIG. 4. It comprises a carriage 1, a lower magnetic head 2 secured to the carriage 1, an upper magnetic head 4 located on the opposite side of a magnetic disk 9 from the lower head 2 and mounted rotatably by a gimbal spring 3 on a spring-loaded arm 5 hinged to the carriage 1 by a leaf spring 6 and having a pivot 7 on which the upper head 4 is rotatable, and a compression spring 8 exerting on the arm 5 a force which is transmitted by the pivot 7 to the upper head 4 to urge the magnetic disk 9 against the lower head 2.
The gimbal spring 3 is provided to compensate for the deflection of the magnetic disk 9, and effectively causes the upper head 4 to fit the disk 9. It is, however, likely that the lower head 2 may be separated from the disk 9 instantaneously, as shown in FIG. 5, resulting in the failure to read or write information on the disk 9. A solution to this problem is proposed in, for example, Japanese Laid-Open Patent Specification No. 167164/1982.
The gimbal spring 3 may, however, undergo the three-dimensional or corrugating deformation which allows the displacement of the upper head 4 in the direction of travel of the disk 9. This results in the generation of a frictional noise due to a stick-slip phenomenon. A number of solutions to this problem have been proposed in, for example, Japanese Laid-Open Patent Specification No. 105358/1981 and Japanese Laid-Open Utility Model Specification No. 144660/1983. None of them has, however, been found satisfactory.
It has been found that the two problems as hereinabove pointed out can be solved if the upper head 4 is fixed to the arm 5, while the lower head 2 is fixed to the carriage 1. Still another problem, however, remains unsolved. Insofar as the leaf spring 6 permits the vertical displacement of the arm 5 at its rear end as shown by a broken line in FIG. 4, it is impossible to avoid the concentration of the force of the compression spring 8 on a limited portion of the disk 9 between the lower head 2 and the upper head 4, and hence the localized wear of the disk 9. A solution to this problem is proposed in, for example, U.S. Pat. No. 4,323,938. It, however, fails to avoid the erroneous mounting of the upper magnetic head and the localized wear of the disk, though it may effectively restrict the vertical displacement of the arm at its rear end. Moreover, it is well known to anybody of ordinary skill in the art that the spherical heads as disclosed by U.S. Pat. No. 4,323,938 fail to cope with the current trend toward a magnetic disk having a narrower track.